Generally, the vehicle wheel bearing apparatus is used to freely rotationally support a wheel hub to mount the wheel, via a rolling bearing, for a driving wheel and a driven wheel. For structural reasons, generally an inner ring rotation type bearing is adopted for a driving wheel. Both inner ring and outer ring rotation type bearings are used for a driven wheel. Double row angular bearings are widely used in such a bearing apparatus. This is due to the fact that it has a desirable bearing rigidity, high durability against misalignment and small rotation torque for superior fuel consumption. On the other hand, double row tapered roller bearings are used for heavy weight vehicles such as off-road cars or trucks.
The vehicle wheel bearing apparatus is broadly classified into a structure of a first generation type where a wheel bearing of double row angular contact ball bearings is fitted between a knuckle, forming a part of a suspension, and a wheel hub. In a second generation type structure, a body mounting flange or a wheel mounting flange is formed directly on the outer circumference of an outer member. In a third generation type structure, one of the inner raceway surfaces is directly formed on the outer circumference of the wheel hub. In a fourth generation type structure, the inner raceway surfaces are formed directly on the outer circumferences of the wheel hub and the constant velocity universal joint.
The wheel bearing apparatus shown in FIG. 21 is a fourth generation type superior for its light weight and small size. It includes a unit of a wheel hub 100, a double row rolling bearing 101, and a constant velocity universal joint 102. The double row rolling bearing 101 has an outer member 103, an inner member 104, and a plurality of balls 105 and tapered rollers 106 contained between the outer and inner members 103, 104. In the descriptions below, the term “outer side” defines a side that is positioned outside of a vehicle body (left-hand side in drawings). The term “inner side” defines the side that is positioned inside of a vehicle body (right-hand side in drawings) when the bearing apparatus is mounted on the vehicle body.
The outer member 103 is formed with a body mounting flange 103c on its outer circumference. The body mounting flange 103c mounts on a knuckle (not shown) forming part of a suspension of the vehicle. Its inner circumference includes double row outer raceway surfaces 103a, 103b. A diameter of the outer side outer raceway surface 103a is set smaller than that of the inner side outer raceway surface 103b. The inner member 104 includes the wheel hub 100, an outer joint member 108 integrally formed with the wheel hub 100, and a separate inner ring 107 press-fit onto the outer joint member 108.
The wheel hub 100 is formed with a wheel mounting flange on its one end. The wheel mounting flange 100b mounts a wheel (not shown). The wheel hub outer circumference has an inner raceway surface 100a arranged opposite to the outer side outer raceway surface 103a of the double row outer raceway surfaces 103, 103b. The outer circumference of the inner ring 107 is formed with an inner raceway surface 107a arranged opposite to the inner side outer raceway surface 103b of the double row outer raceway surfaces 103a, 103b. 
The constant velocity universal joint 102 includes the outer joint member 108 with a cup-shaped mouth portion 109 and a shoulder portion 110. The shoulder portion 110 forms a bottom portion of the mouth portion 109. The inner circumference of the outer joint member 108 is formed with curved track grooves 108a. The inner ring 107 is press-fit onto the outer circumference of the mouth portion 109 and axially immovably secured by a snap ring 111.
The plurality of balls 105 are freely rollably contained between the outer side outer and inner raceway surfaces 103a, 100a. The plurality of tapered rollers 106 are freely rollably contained between the inner side outer and inner raceway surfaces 103b, 107a. The pitch circle diameter of the outer side balls 105 is set smaller than that of the inner side tapered rollers 106. This enables the fundamental rated load of the inner side rolling elements, which a larger load is applied than a load applied to the outer side rolling elements, to be larger than the fundamental rated load of the outer side rolling elements. Thus, this enables the life of the outer side and inner side rolling elements to be substantially the same to each other and to obtain a smart design (see e.g. Japanese Laid-open Patent publication No. 91308/1999).
In such a wheel bearing apparatus, since the inner ring 107 is secured on the mouth portion 109 of the outer joint member 108, the size of the apparatus can be reduced in its axial direction. However, since the outer diameter of the outer member 103 is enlarged, not only is the reduction of weight of the wheel bearing apparatus hampered but also design modifications of related parts, such as a knuckle, are required. In order to solve such a problem, the wheel bearing apparatus shown in FIG. 22 has been proposed.
This wheel bearing apparatus is formed by a double row angular contact ball bearing with an outer member 112 formed with a body mounting flange 112a on its outer circumference. The body mounting flange 112c is mounted on a knuckle (not shown) of a vehicle. Its inner circumference surface has double row outer raceway surfaces 112a, 112b. An inner member 116 includes a wheel hub 114 formed with a wheel mounting flange 113 on one of its ends. The wheel mounting flange 113 mounts a wheel (not shown). The wheel hub outer circumference has an inner raceway surface 114a arranged opposite to the outer side outer raceway surface 112a of the double row outer raceway surfaces 112a, 112b. A cylindrical portion 114b axially extends from the inner raceway surface 114a. An inner ring 115, formed with an inner raceway surface 115a, is arranged opposite to the inner side outer raceway surface 112b of the double row outer raceway surfaces 112a, 112b. Double row balls 117, 118 are freely rollably contained between the outer raceway surfaces and inner raceway surfaces. Cages 119, 120 freely rollably hold the double row balls 117, 118.
The inner ring 115 is axially secured by a caulked portion 114c. The caulked portion 114c is formed by radially outwardly plastically deforming the end of the cylindrical portion 114b of the wheel hub 114. Seals 121, 122 are mounted within annular openings formed between the outer member 112 and the inner member 116. The seals 121, 122 prevent leakage of lubricating grease sealed within the bearing and the entering of rain water or dusts from the outside into the bearing.
In this wheel bearing apparatus, a pitch circle diameter D1 of the outer side row of balls 117 is set larger than a pitch circle diameter D2 of the inner side row of balls 118. Accordingly, the diameter of the inner raceway surface 114a of the wheel hub 114 is larger than that of the inner raceway surface 115a of the inner ring 115. The diameter of the outer side outer raceway surface 112a of the outer member 112 is larger than that of the inner side outer raceway surface 112b. In addition, the number of the outer side balls 117 is larger than that of the inner side balls 118. By setting the relation between the pitch circle diameters D1, D2 as D1>D2, it is possible to increase the rigidity of the wheel bearing apparatus not only in the case of running in a straight way but also in the case of running in a curved way and thus to extend the life of the wheel bearing apparatus (see e.g. Japanese Laid-open Patent publication No. 108449/2004).